You can test the login with a web browser.
After successful login, it should display something like “This is the WebDAV interface. It can only be accessed by WebDAV clients such as the Nextcloud desktop sync client.”
The Developer Tools of your web browser may be of help with the debugging
OK so it is probably the 2fa blocking the login. I will regenerate an app password. Thank you for the suggestion.
Morality never update your setup if it is working